This invention relates to a method of making heat-bonded porous structures from recycled plastics and to such structures.
WO2004/082912 discloses a method of making drainage elements from recycled plastics. In the method, chopped waste thermoplastic plastics are supplied to an agglomerator which heats and agglomerates the plastics into noodles. The heated noodles are then conveyed from the agglomerator via conveyors into a chute of a compactor/shaper funnel. The agglomerated plastics meld together at their contact faces when sufficiently connected and pressed together in the compactor/shaper funnel to form an integral continuous compacted ribbon of melded noodles with spaces therebetween. The ribbon exits through an outlet of the compactor/shaper funnel, where it is turned ninety degrees to be put onto a belt. The belt speed affects the rate at which the compaction occurs. The ribbon is then cooled and chopped into bats. The width and thickness of the ribbon and therefore the bats are limited by the shape and size of the compactor/shaper funnel, and the ninety degree turn when exiting the compactor/shaper funnel. The bats are disclosed to be about 250 mm wide and 50 mm thick, and this size is constant as is further described below.
Because bats are commonly used for drainage or attenuation, it is common to require very large cross-sectional areas of the bats, for example 500 mm wide and 500 mm thick. Using the methods disclosed in WO2004/082912 to form the bats, many bats must be formed and then stacked together to meet the size and/or shape requirements. Thus, the method to form such a drainage area from the bats disclosed in WO2004/082912 is time consuming, and can result in stability issues if not stacked or secured together properly.
In other applications, such as soak away or water treatment applications, very small pieces or different sizes of drainage material are required, for example pieces about the size of a tennis ball. To make such a piece from WO2004/082912, a bat would need to be formed and then cut down to a desired size, requiring a number of extra steps to result in the desired finished product. Simply making the compactor/shaper funnel smaller may result in insufficient weight of the heated malleable noodles within the small compactor/shaper funnel to allow melding of the noodles and pushing the noodles through the compactor/shaper funnel onto the conveyor. If a larger bat were desired, the amount of heat required would likely cause the center noodles to coalesce into a solid non-porous block and lost the ability to hold open spaces between the noodles.
Additionally, some drainage structures require large open spaces and/or interconnections for connecting together. The methods disclosed in WO2004/082912 would not be able to produce such structures.